The present invention relates to hydraulic fluids useful in a wide variety of applications where a hydraulic fluid is employed to transmit fluid pressure. The invention relates more particularly to hydraulic fluids which are intended to be used in locations near environmental water sources, such as streams, rivers, lakes, and oceans. The fluids according to the invention possess strong dispersant qualities sufficient to leave no sheen in cases of their accidental release to environmental water sources. The hydraulic fluids of the invention are extremely low in toxicity to aquatic life and thus pose a minimal risk to ecosystems.
Hydraulic fluids are used in systems which are generally well-known in the art for providing a means for transmitting any applying large forces to moveable mechanical components, while retaining a great degree of flexibility and control. Such systems are used in most forms of mechanized motion to transmit, transform and control mechanical work. They are part of a major technical discipline known to those skilled in the art as xe2x80x9cfluid power technologyxe2x80x9d.
A typical hydraulic system includes the following components: 1) a force-generating unit that converts mechanical energy into hydraulic energy, such as a pump; 2) a hydraulic fluid; 3) piping for transmitting fluid under pressure; 4) a unit that converts the hydraulic energy of the fluid into mechanical work, such as an actuator or fluid motor; 5) A control circuit with valves that regulate flow, pressure, direction of movement, and applied forces; and 6) a fluid reservoir that allows for filtration and/or separation of any particulate debris or water before returning the clean fluid to the system. Thus, the fluid is in contact with each mechanical component of the system used for transmitting mechanical energy, including metallic components which may come into direct physical contact with one another.
It is generally accepted that hydraulic fluids can be defined as any liquids which are necessary for the proper functioning of a hydraulic system. The primary function of the fluid is to transmit force which is applied at one point in the system to some other location in the system, and to quickly produce desired changes in the direction or the magnitude of that force. Hydraulic systems using such suitable fluids are very common and have numerous applications in industry and daily life, including uses in automotive systems such as brakes, clutches, and transmissions, in industrial equipment for applications such as pressing, molding, mining, metal forming and positioning, excavation equipment such as backhoes, in devices such as elevators, and in the transportation industry for many control and motive systems in ships and aircraft. The art of hydraulic fluid formulation contains several technical references which describe hydraulic fluids which are based upon hydrocarbon oils. Such systems include those described in U.S. Pat. Nos. 2,403,067; 2,892,854; 2,967,831; 4,151,101; 4,208,293; 4,293,432; and 4,557,846, the entire contents of each of which are herein incorporated by reference thereto.
For optimal functioning, a hydraulic fluid must be relatively incompressible and must flow readily. In addition, there are a number of secondary functions provided by hydraulic fluids, which functions are extremely important for successful system operation, including adequate lubricity for moving parts, stability under anticipated conditions of use, compatibility with materials used to construct the hydraulic system, and the fluids should have the ability to protect system components against chemical reaction with materials which may enter the system.
Additives to the fluid which protect system components against chemical reaction are frequently called xe2x80x9ccorrosion inhibitorsxe2x80x9d. Corrosion can result from the formation of reactive decomposition products of the fluid itself, from components of the fluid (e.g., additives) which are corrosive, or from the entry of contaminants into the hydraulic system.
In the case of hydraulic fluids which are based upon hydrocarbon oils, an environmental problem arises when such fluids come into contact with environmental water sources in that at least a portion of the oils tend to float on the surface of the water and create an unsightly sheen which may extend or be visible for great distances. This is known to be the case even when the total amount of the oil accidentally spilled is relatively small, and the concentration of the oil on surface of the water poses potential harm to aquatic life forms. Such situations have in the past commonly arisen for ships at sea, when there is a leak of a hydraulic fluid used in one of the ship""s operating systems, and in general in any situation where hydraulic fluids are used in close proximity to environmental water sources, such as oil drilling platforms, paper mills, and amusement parks. As the United States government has promulgated rules concerning releases of materials that useful as hydraulic fluids in Title 40 of the Code of Federal Regulations, section 110, an increased level of awareness of issues surrounding spills of hazardous oils has become manifest in recent years. In response with such rulemaking, many users of hydraulic oils have undertaken to employ special precautions in their handling and use of hydraulic fluids. Clearly, if formulations of hydraulic fluids were available that do not form a sheen on the surface of water into which such fluids came into contact and which are environmentally benign, such fluids would be welcomed by all persons to whom such fluid types are of practical use.
The problems associated with the use of and release into environmental waters of water-immiscible, hydrocarbon oil based hydraulic oil formulations may be eliminated by the use of a liquid composition according to the present invention, which comprises water-soluble polyoxyalkylene glycols having either of the general formulae: 
in which x is selected from any whole integer 1, 2, 3, 4, or 5; y is selected from 1 or 2; and m is an integer sufficient to provide a molecular weight in the range of between about 450 and 5000. Such materials are used in combination with a carboxylic acid having between about 6 and 18 carbon atoms per molecule of carboxylic acid, an amine, and optionally, an extreme pressure additive to provide a composition according to the invention. Since the physical properties and performance characteristics required of hydraulic fluids are similar to those required by gear oils in many applications, the formulations of the invention are of widespread applicability.
The present invention comprises multi-component liquid compositions of matter which comprise a predominant amount of a water-soluble polyoxyalkylene glycol having a pre-selected molecular weight of any value in the range of between 450 and 5000. When formulated according to the present invention, the functional fluids disclosed provide an excellent viscosity index which is greater than about 160. An especially preferred family of water soluble polyoxyalkylene glycol useful in the compositions of the present invention may also be one produced from alkoxylation of n-butanol with a mixture of alkylene oxides to form a random alkoxylated product which may be described by the either of the general formulae: 
in which x may independently be any whole integer between 0 and 5, including 0 and 5; y may independently be any integer between 0 and 2, including 0 and 2; may independently be any whole integer between 1 and 5, including 1 and 5; p may independently be either 1 or 2; wherein m is an integer within the range suitable to provide a molecular weight of between 450 to 5000.
Functional fluids according to the invention possess a pour point of less than about xe2x88x9220xc2x0 C., and exhibit compatibility with a wide range of anti-wear additive and extreme pressure additives. The formulations according to the invention also are devoid of fatigue failure that is normally expected by those of ordinary skill in the art when dealing with polar lubricant base stocks. This is evident from the comparison of the performance of similarly formulated butyl (polyoxypropylene only) based hydraulic fluids with those of the preferred form of the invention which are butyl (oxyethylene/oxypropylene).
It has been unexpectedly discovered that when normally highly oil soluble extreme pressure additives are used in a formulation according to the invention and when a formulation according to the invention is spilled into a body of water, no sheen or oily layer on the surface of the water is visually detectable and the water surface is not discolored in any noticeable way. Such normally highly oil soluble extreme pressure additives include triisopropylphenyl phosphate.
Polyoxyalkylene glycols useful in the present invention may be produced by a well-known process for preparing polyalkylene oxide having hydroxyl end-groups by subjecting an alcohol or a glycol ether and one or more alkylene oxide monomers such as ethylene oxide or propylene oxide to addition polymerization while employing a strong base such as potassium hydroxide as a catalyst. In such process, the polymerization is commonly carried out under a catalytic concentration of 0.3 to 1.0% by mole of potassium hydroxide to the monomer(s) and at high temperature, as 100 degrees C. to 160 degrees C. It is well known fact that the potassium hydroxide being a catalyst is for the most part bonded to the chain-end of the produced polyalkylene oxide in a form of alkoxide in the polymer solution so obtained.
Useful as components in a formulation according to the present invention are those polyoxyalkylene glycols described by either of the general formulae: 
in which x may independently be any whole integer between 1 and 5; and y may independently be either 1 or 2; and m is sufficient to provide a material having a molecular weight in the range of 450 to 5000.
An especially preferred family of water soluble polyoxyalkylene glycol useful in the compositions of the present invention may also be one produced from alkoxylation of n-butanol with a mixture of alkylene oxides to form a random alkoxylated product which may be described by the either of the general formulae: 
in which x may independently be any whole integer between 0 and 5, including 0 and 5; y may independently be either 1 or 2; z may independently be any whole integer between 1 and 5, including 1 and 5; p may independently be 1 or 2; and wherein m is an integer sufficient to provide a molecular weight in the range of 450 to 5000, subject to the provisos that at least one of x and z is equal to at least one and that at least one of y and p is equal to at least one.
It has been surprisingly found that hydraulic fluids prepared in accordance with the present invention which are made using a mixture of propylene oxide and ethylene oxide and n-butanol exhibit surprisingly low levels of toxicity while retaining adequate lubricity properties and dispersability characteristics for hydraulic fluid applications. Thus, preferred polyoxyalkylene glycols useful in accordance with the present invention are those prepared using n-butanol as a starting material, and subjecting n-butanol to polymerization conditions in the presence of a mixture of propylene oxide and ethylene oxide, in which the amount of propylene oxide in the gaseous mixture is preferably between 35.00% and 65.00% by weight based upon the total weight of the mixture, including every hundredth percentage therebetween, more preferably between 35.00% and 65.00% by weight based upon the total weight of the gaseous mixture, including every hundredth percentage therebetween, and most preferably between 45.00% and 55.00% by weight based upon the total weight of the gaseous mixture, including every hundredth percentage therebetween.
In order to produce a polyoxyalkylene glycol monobutyl ether with minimum polyoxyalkylene glycol contamination, it has been found beneficial to use an initiator for the polymerization, with a butanol-derived species that already contains one, two, or three alkylene oxide units per molecule such as a glycol ether represented by the formula: 
wherein R1 is methyl or hydrogen and wherein m is independently selected from 1, 2, or 3 being especially preferred. These glycol ether initiators have a sufficiently low vapor pressure that allows the stripping of water from a mixture of the initiator and potassium hydroxide, and prevents unwanted polyoxyalkylene glycol by-product formation. Various suitable polyoxyalkylene glycols monobutyl ether for this invention are available from Huntsman Petrochemical Corporation having an office at 7114 North Lamar Blvd. in Austin, Tex. under the JEFFOX(copyright) tradename. Products of these alkoxylation reactions such as JEFFOX WL-170, JEFFOX(copyright) WL-260, JEFFOX(copyright) WL-660, and JEFFOX(copyright) WL-5000 having molecular weight ranges of about 450 to 5000 are useful as a component of formulations useful as a hydraulic fluid. JEFFOX(copyright) WL-170, has a number average molecular weight of about 450 and is useful as a component of formulations useful as a hydraulic fluid. JEFFOX(copyright) WL-260 has a number average of about 750 and is useful as a component of formulations useful as a hydraulic fluid. JEFFOX(copyright) WL-660 has a number average molecular of about 1800 and is useful as a component of formulations useful as a hydraulic fluid. JEFFOX(D WL-5000 has a number average of about 4200 and is useful as a component of formulations useful as a hydraulic fluid.
For purposes of this specification and the appended claims the words xe2x80x9cextreme pressure additivexe2x80x9d means those particular chemical materials generally regarded by artisans of ordinary skill in the lubrication or tribology arts as being useful as extreme pressure additives for ho lubricants, which include without limitation: sulfurized olefins, dithiophosphate salts of transition metals including without limitation such exemplary salts as zinc dithiophosphate and copper dithiophosphate, derivatives of alkylated phenols including mono or poly-alkyl phenol phosphates, organic phosphates, organic sulfur and chlorine compounds, sulfurized fats, other phosphates, sulfides, di-sulfides, and polysulfides. It is most preferred, however, that the extreme pressure additive comprise a trialkyl phenol phosphate such as those available under the tradename Durad 110, Durad 150, Durad 220, and Durad 300 from Great Lake Chemical Corp., of West Lafayette, Ind., USA; or those available under the trade name of IRGALUBE(copyright) from Ciba Specialty Chemicals of Basel, Switzerland. Durad 300 is an especially preferred trialkyl phenol phosphate.
Compositions according to the invention also include an amine component, the function of which is to control corrosion by maintaining the overall pH of the lubricant in the alkaline range. Preferred amines for this use include primary amines, secondary amines, tertiary amines, cycloalkyl amines, aromatic amines, diamines, polyalkylene polyamines, and include all amines generally regarded by one of ordinary skill in the art as being useful for controlling corrosion of metal surfaces by either neutralizing acids produced during equipment operation or by acting as a metal deactivator. One especially preferred amine for use in compositions according to the invention is DIGLYCOLAMINE(copyright) Agent amine product because of its ability to impart both corrosion resistance and favorable toxicology profile. DIGLYCOLAMINE(copyright) Agent is available from Huntsman Petrochemical Corporation of Austin, Tex.
As mentioned, fluid compositions according to the invention exhibit an especially favorable low toxicity with respect to aquatic life, which is important from an environmental standpoint because leaks of functional fluids into the environment often occur at some point during either their storage, transportation, or use. Table I provides comparative data between monobutyl ethers which have been addition polymerized with different olefin oxides to different molecular weights. The olefin oxides used were propylene oxide (xe2x80x9cPOxe2x80x9d) and ethylene oxide (xe2x80x9cEOxe2x80x9d). In one set of data, pure propylene oxide was used. In another set of data, a 50:50 mixture (molar basis) of propylene oxide and ethylene oxide was used in the polymerization. A third set of data was obtained for the butane di-ol based products in which a 75:25 molar mixture of EO to PO was employed during the polymerization.
As is evident from the data in table I, polyoxyalkylene glycols produced using substantial amounts of ethylene oxide during the addition polymerization exhibit a much greatly reduced degree of toxicity with respect to those polyoxyalkylene glycols produced using only propylene oxide during the addition polymerization. Thus, the predominant ingredient in formulations according to this invention are seen to be of very low toxicity. Poly-G(copyright) is a trademark of Olin Corporation, and the various product equivalents indicate that these materials are available from Olin Corporation of Norwalk, Conn. The prefix WS, WI, and WT each mean water-soluble, water-insoluble, and water-thickening, respectively, and the number after the prefix indicates the approximate viscosity in Saybolt Universal Seconds (SUS) at 38xc2x0 C. (100xc2x0 F.).
Formulations according to the invention will generally comprise the following components in the listed amounts, wherein all parts and/or percentages are by weight: Carboxylic acid: 1 to 2%; Amine: 0.75 to 1.6%; extreme pressure additive: 1 to 1.5%; and optional fire retardant at about 0.5%. Formulations of finished products according to this invention are set for the below. In general, it is preferred in accordance with the invention to employ polyoxyalkylene glycols having a molecular weight in the range of 750-2000 for use in fluids to be used where a hydraulic fluid is needed, and it is preferable to use a polyoxyalkylene glycol having a molecular weight in the range of 2000-5000 for use in gear oils.